Any advice on a good TT for my 2012 Expedition?

I tow with an 07 expedition, same specs. Our 24' TT fully loaded with a full tank of fresh water is about 6k. I use a WDH. On the flat highway with no wind it cruises along at the speed limit nicely, but definitely struggles over the hills. Never had an issue getting where we want to go but we aren't getting there fast. I would not want to go any heavier than we are now and will upgrade the TV before we move to any other trailer. Good luck!